RU2650659C2 - FABRICABLE, HIGH STRENGTH, OXIDATION RESISTANT Ni-Cr-Co-Mo-Al ALLOYS - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, in particular to fabricable, high strength alloys that can be used to manufacture gas turbine engine parts. Nickel-chromium-cobalt-molybdenum-aluminum alloy contains, wt%: from 15 to 20 chromium, from 9.5 to 20 cobalt, from 7.25 to 10 molybdenum, from 2.72 to 3.9 aluminum, up to 10.5 iron, up to 0.15 carbon, up to 0.015 boron, up to 0.75 titanium, up to 1 niobium, up to 1.5 tantalum, up to 1 hafnium, up to 2 tungsten, up to 1 manganese, up to 0.6 silicon, up to 0.06 zirconium, up to 0.05 magnesium, up to 0.05 calcium, up to 0.05 rare earth element, up to 0.5 copper, up to 0.015 sulphur, up to 0.03 phosphorus, with the remaining amount is nickel and impurities.

EFFECT: alloy is fabricable, has high resistance to fracture and high resistance to oxidation of up to 2100°F (1149°C).

17 cl, 12 tbl

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of US Provisional Patent Application Serial No. 61/790137, filed March 15, 2013, and incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to easily machined, high-strength alloys for use at elevated temperatures. In particular, it relates to alloys that have excellent oxidation stability, high resistance to creep fracture, and sufficient processability to ensure operability in the combustion chambers of gas turbine engines and other environments requiring high temperatures.

BACKGROUND

A variety of alloys are available on the market for sheet parts in gas turbine engines. According to their key characteristics, these alloys can be divided into various series. It should be noted that the following discussion relates to alloys that can be cold worked / welded, which implies that they can be made as a cold rolled sheet, cold formed to form a fabricated part, and welded.

Gamma-bar phase alloys. These include R-41 alloy, Waspaloy alloy, 282® alloy, 263 alloy, and others. These alloys are characterized by their high resistance to creep fracture. However, the maximum operating temperatures of these alloys are limited by the gamma-bar phase solvus temperature, and they, as a rule, are not used at temperatures above 1600-1700 ° F (from 871 to 927 ° C). In addition, while the oxidation resistance of these alloys is quite good in the range of operating temperatures, it decreases at higher temperatures.

Alloys forming aluminum oxide. These include alloy 214® and alloy HR-224®, but not oxide dispersion hardening (ODS) alloys (which do not have the required machinability). The alloys in this series have excellent oxidation resistance at temperatures up to 2100 ° F (1149 ° C). However, their use in structural parts is limited due to poor resistance to creep fracture at temperatures higher than about 1600-1700 ° F (from 871 to 927 ° C). It should be noted that these alloys will also form a strengthening gamma phase, but this phase is unstable in the range of higher temperatures.

Solidified alloys. These include alloy 230®, alloy HASTELLOY® X, alloy 617, and others. As their name implies, the high resistance of these alloys to creep fracture is determined mainly by the effect of hardening of the solid solution, as well as the formation of carbides. This hardening remains effective even at very high temperatures - for example, well above the maximum temperature for alloys forming the gamma-ray phase. Many of the hardened alloys have very good oxidation stability due to the formation of a chromium oxide protective film. However, their oxidation resistance is not comparable with alloys forming aluminum oxide, in particular at very high temperatures, such as 2100 ° F (1149 ° C).

Alloys with nitride dispersion hardening. These include NS-163® alloy, which has very high creep resistance to temperatures up to 2100 ° F (1149 ° C). While the creep resistance to creep of the NS-163 alloy is better than that of alloys based on solid solutions, its oxidation resistance is only similar. It does not have excellent oxidation stability for aluminum oxide forming alloys.

From the discussion above, it is clear that there is no alloy suitable for cold working / welding on the market that combines both high creep resistance and excellent oxidation resistance. However, with the constant desire without interruption to increase the operating temperatures of gas turbine engines more and more, it is obvious that alloys that combine these qualities would be highly desirable.

SUMMARY OF THE INVENTION

The main objective of the present invention is the creation of easily machined alloys that have both high resistance to creep fracture and excellent oxidation resistance. This high-value combination of properties was not found in the prototype (or is not expected from it). The composition of the alloys that were presented as having these properties is as follows: from 15 to 20 wt.% Chromium (Cr), from 9.5 to 20 wt.% Cobalt (Co), from 7.25 to 10 wt.% Molybdenum (Mo), from 2.72 to 3.9 wt.% Aluminum (Al), and carbon (C), present in an amount up to 0.15 wt.%. Elements of titanium (Ti) and niobium (Nb) may be present, for example, to provide hardening, but their quantity should be limited due to their harmful effect on certain aspects of manufacturability. In particular, an excessive content of these elements can increase the susceptibility of the alloy to cracking during deformation aging. If present, titanium should be limited to a content of not more than 0.75 wt.%, And niobium to a content of not more than 1 wt.%.

It was unexpectedly discovered that the presence of elements of hafnium (Hf) and / or tantalum (Ta) is associated with an even longer service life of these alloys with respect to creep fracture. Therefore, one or both of the elements can be added to these alloys to further improve the creep resistance to fracture. Hafnium can be added at levels up to about 1 wt.%, While tantalum can be added at levels up to about 1.5 wt.%. For maximum efficiency, the sum of the tantalum and hafnium levels should be between 0.2 wt.% And 1.5 wt.%.

To ensure workability, the amounts of certain elements that may or may not be present (more specifically, aluminum, titanium, niobium, and tantalum) should be limited in such a way as to satisfy the following additional ratio (where the amounts of elements are given in wt.%):

Al + 0.56Ti + 0.29Nb + 0.15Ta ≤ 3.9 [1]

In addition, boron (B) may be present with a small but effective trace content of up to 0.015% by weight, to obtain certain favorable properties known in the art. Tungsten (W) may be present in this alloy to a content of about 2% by weight. Iron (Fe) may also be present as an impurity, or may be added intentionally to reduce the total cost of raw materials. However, iron should not be present in an amount of more than about 10.5 wt.%. If niobium and / or tungsten are present as minor secondary elements, the iron content should be even more limited to 5% by weight or less. In order to be able to remove oxygen (O) and sulfur (S) during the smelting process, these alloys typically contain small amounts of manganese (Mn) up to about 1 wt.%, And silicon (Si) up to about 0.6 wt.%, And possibly traces of magnesium (Mg), calcium (Ca) and rare earth elements (including yttrium (Y), cerium (Ce), lanthanum (La), etc.) up to about 0.05 wt.% everyone. Zirconium (Zr) may be present in the alloy, but its content in these alloys must be kept at less than 0.06% by weight to maintain workability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The authors of the present invention are alloys based on Ni-Cr-Co-Mo-Al, which contain from 15 to 20 wt.% Chromium, from 9.5 to 20 wt.% Cobalt, from 7.25 to 10 wt.% Molybdenum from 2.72 to 3.9 wt.% aluminum, together with typical impurities, iron in an acceptable amount of up to 10.5 wt.%, additives of minor elements, and the remaining amount of nickel, which are easily processed, have high creep resistance and excellent oxidation resistance to temperatures as high as 2100 ° F (1149 ° C). This combination of properties is favorable for the various components of gas turbine engines, including, for example, combustion chambers.

Based on an understanding of the requirements for the combustion chambers of future gas turbine engines, an alloy with the following characteristics would be highly desirable: 1) excellent oxidation resistance at temperatures as high as 2100 ° F (1149 ° C), 2) workability so good that it can be made in the form of a deformable sheet, being suitable for cold forming, welding, etc., 3) high resistance to creep fracture, as good or better than conventional industrial alloys, such as HASTELLOY X , and 4) good heat resistance at elevated temperatures. In the past, for a long time, attempts to develop an alloy that combines all four characteristics were unsuccessful, and accordingly, there is no commercially available alloy with all four of these qualities on the market.

The authors of the present invention tested 30 experimental alloys, the compositions of which are shown in Table 1. The experimental alloys were labeled from A to Z and from AA to DD. The experimental alloys had a Cr content that varied from 15.3 to 19.9% by weight, as well as a cobalt content ranging from 9.7 to 20.0% by weight. The molybdenum content ranged from 5.2 to 12.3 wt.%. The aluminum content ranged from 1.93 to 4.30 wt.%. The iron content ranged from less than 0.1 up to 10.4 wt.%. In certain experimental alloys, additives of minor elements were present, including titanium, niobium, tantalum, hafnium, tungsten, yttrium, silicon, carbon, and boron.

All alloy tests were conducted on sheet material with a thickness of from 0.065 inches to 0.125 inches (1.6 to 3.2 mm). The experimental alloys were smelted in a vacuum induction furnace, and then remelted in an electroslag furnace, with a smelting mass of 30 to 50 pounds (13.6 to 27.2 kg). The ingots thus obtained were hot forged and rolled to an intermediate sheet thickness. The sheets were annealed, quenched with water and cold rolled to obtain sheets with the desired thickness. Intermediate annealing of the cold rolled sheet was necessary during the manufacture of the sheet with a thickness of 0.065 inches (1.6 mm). If necessary, cold-rolled sheets were annealed to obtain a fully crystallized, equiaxed grain structure with ASTM grain sizes between 3½ and 4½.

To evaluate key characteristics (oxidation resistance, machinability, creep resistance, and heat resistance), four different types of tests were carried out on experimental alloys to establish their suitability for the intended application. The results of these tests are described in the sections below.

Oxidation resistance

Oxidation resistance is the most important characteristic for a modern high-temperature alloy. Temperatures in the combustion chamber of a gas turbine engine can be very high, and there is always a tendency in industry for more and more high temperatures. An alloy having excellent oxidation resistance at temperatures up to 2100 ° F (1149 ° C) would be a good candidate for use in many applications. The oxidation resistance of nickel-based alloys to a very large extent depends on the nature of the oxides that form on the surface of the alloy upon thermal exposure. Generally, it is preferable to form a protective surface layer, such as chromium-rich and aluminum-rich oxides. The alloys that form such oxides are often called chromium oxide or alumina formers, respectively. The vast majority of wrought high-temperature nickel alloys are chromium oxide formers. However, there are few alumina formers on the market. One such example is the HAYNES® 214® alloy. Alloy 214 is well known for its excellent oxidation resistance.

In order to determine the oxidation resistance of the experimental alloys, an oxidation test was carried out on most alloys in an air stream at 2100 ° F (1149 ° C) for 1008 hours. Five industrial alloys were also tested with these samples: HAYNES 214 alloy, 617 alloy, 230 alloy, 263 alloy and HASTELLOY X alloy. The samples were subjected to weekly cyclic cooling to room temperature. At the end of 1008 hours, the scale was removed from the samples and they were sent for metallographic examination. The data in Table 2 represent the results of oxidation tests. The recorded value represents the average metal damage, which is the sum of the metal loss plus the average internal penetration of the oxidizing effect. Details of this type of test can be found in International Journal of Hydrogen Energy, Volume 36, 2011, pp. 4580-4587. For the purposes of the present invention, an average metal damage value of 2.5 mils / surface (64 μm / surface) or less was the preferred technical requirement, and an appropriate indicator of whether the alloy could be considered as having “excellent” oxidation resistance. Indeed, a metallographic study of alloys with less than this level of exposure confirms their desirable oxidation resistance characteristics. Certain elements / impurities present in small quantities could possibly reduce (but still at an acceptable level) oxidation resistance, so the value of the average metal damage could probably be as high as 3 mils / surface (76 μm / surface), while still maintaining excellent oxidation resistance.

table 2
Oxidation Test Results at 2100 ° F (1149 ° C) Alloy Averaged metal damage (mil / surface) (microns / surface) A 0.9 23 B 0.9 23 C 0.7 eighteen D 1,0 25 E 0.6 fifteen F 0.9 23 G 0.9 23 H 0.4 10 I 0.6 fifteen J 0.6 fifteen K 1.8 46 L 0.7 eighteen M 1,5 38 N 0.5 13 O 0.6 fifteen

P 0.5 13 Q 0.4 10 R 0.9 23 S 0.6 fifteen T 1,1 28 U 1.4 36 V 2,3 58 W 0.5 13 X 1,6 41 Z 0.5 13 CC 4.4 112 263 16.5 419 214 1.3 33 617 5.1 130 230 4.8 122 HASTELLOY X 12.0 305

The oxidation results of experimental alloys were very expressive. All of the tested experimental alloys (with the exception of CC alloy) had an average metal damage of 2.3 mils / surface (58 μm / surface). Therefore, all of these alloys (with the exception of CC alloy) had acceptable oxidation resistance for the purposes of the present invention. When considering industrial grade alloys, all experimental alloys were comparable to HAYNES 214, an aluminum oxide-forming alloy, which had an average metal damage value of 1.3 mils / surface (33 μm). In contrast, all chromium oxide-forming alloys 617, alloy 230, HASTELLOY X alloy, and alloy 263 had much higher levels of oxidative attack, with average metal damage values of 5.1, 4.8, 12.0, and 16.5 mils / surface (130, 122, 305, and 419 μm), respectively. The excellent oxidation resistance of the experimental alloys appears to be due to the critical amount of aluminum, which is 2.72% or more by weight for all experimental alloys other than the CC alloy. Alloy CC had an Al value of only 1.93% by weight, indicating that this was too low an Al content for the desired excellent oxidation resistance. Similarly, the levels of Al in the four chromium oxide-forming industrial alloys were quite low (the highest for alloy 617 at 1.2 wt.% Al). In contrast, the alumina-forming alloy 214 has an Al content of 4.5% by weight. Thus, all of the nickel-based alloys tested in this program with an Al content of 2.72 wt.% Or more were found to have excellent oxidation resistance, while alloys with lower Al contents were not. Therefore, for an alloy considered to be in accordance with the present invention, the Al content in the alloy should be greater than or equal to 2.72 wt.%.

Machinability

One of the requirements for the alloys according to the present invention is that they be machinable. As discussed previously, for alloys containing significant amounts of certain elements (such as aluminum, titanium, niobium and tantalum), the presence of good machinability is closely related to the resistance of the alloy to cracking during deformation aging. The resistance of the experimental alloys to cracking during strain aging was measured using the modified CHRT test (tensile test with variable heating rate), described by Metzler in the appendix to the Welding Journal, October 2008, p. 249s-256s. This test was developed to determine the relative resistance of alloys to cracking during strain aging. One test option is described in US Patent No. 8066938. In the modified CHRT test, the width of the meter section is variable, and the test is performed on a thermomechanical simulator rather than on a screw-type tensile test apparatus. The results of the two different test forms are expected to be qualitatively similar, but the quantitative results in absolute terms will be different. The results of the modified CHRT test conducted on experimental alloys of the inventors of the present invention are shown in Table 3. The test was carried out at a temperature of 1450 ° F (788 ° C), and the recorded values of CHRT ductility were measured as elongation in excess of 1.5 inches (38 mm ) The ductility according to the CHRT test of experimental alloys ranged from 5.9% for DD alloy to 17.9% for X alloy.

Table 3 also shows the results of the modified CHRT test for three industrial alloys, as published by Metzler in the appendix to the Welding Journal, October 2008, pp. 249s-256s. Both ductility values according to the CHRT test for alloy R-41 and Waspaloy were less than 7%, while the value for alloy 263 was 18.9%. Alloy R-41 and Waspaloy, being weldable, are both known to be susceptible to cracking during deformation aging, while alloy 263 is considered to be easily weldable. On this basis, the alloys according to the present invention should have ductility values for the modified CHRT test of more than 7%. Of the experimental alloys, only O and DD alloys had a plasticity value of less than 7% according to the modified CHRT test; therefore, alloys O and DD cannot be considered as alloys according to the present invention.

Table 3
Modified CHRT Test Results Alloy Plasticity according to the modified CHRT test (%) A 13.0 B 11.6 C 7.7 D 13.3 E 13.6 F 8.9 G 10.3 H 8.7 I 9,4 J 10,2

K 8.6 L 8.0 M 9.7 N 10.0 O 6.3 P 9.3 Q 10,2 R 10.8 S 9,4 T 9.9 U 9.5 V 15.1 W 16.3 X 17.9 Y 13.5 Z 11.9 AA 10.5 BB 8.9 CC 15.3 DD 5.9 R-41 6.9 Waspaloy 6.8 263 18.9

It was found that for these Ni-Cr-Co-Mo-Al-based alloys, cracking resistance during deformation aging could be associated with the total amount of gamma-bar-phase forming elements Al, Ti, Nb and Ta. Therefore, the combined amount of these elements present in the alloy should satisfy the following ratio (where the number of elements is given in% by weight):

Al + 0.56Ti + 0.29Nb + 0.15Ta ≤ 3.9 [1]

The values of the left side of equation 1 are shown in Table 4 for all experimental alloys. All alloys where the "Al + 0.56Ti + 0.29Nb + 0.15Ta" value was less than or equal to 3.9 can be shown to have ductility according to the modified CHRT test of more than 7%, and therefore meet the requirement for resistance to strain aging cracking according to the present invention. Only O, Q, and DD alloys were found to have values in excess of 3.9. For O and DD alloys, the values of 3.93 and 4.54 may be consistent with poor ductility according to the modified CHRT test. On the other hand, alloy Q was found to have acceptable ductility by the modified CHRT test. This appears to be the result of a high Fe content in the alloy. As is known, Fe additives inhibit the formation of the gamma-ray phase, and thus could help improve ductility by the modified CHRT test. However, a lower amount of gamma-bar phase forming elements is generally favorable for workability. Therefore, the value of "Al + 0.56Ti + 0.29Nb + 0.15Ta" should be kept lower than or equal to 3.9 for all alloys according to the present invention. It should be noted that one consequence of this is that the maximum aluminum content in the alloys according to the present invention should be 3.9% (which corresponds to a situation where all elements of titanium, niobium and tantalum are absent).

Table 4
Experimental alloys - the value of equation [1] (left side) Alloy Al + 0.56Ti + 0.29Nb + 0.15Ta A 3.78 B 3.70 C 3.78 D 3.68 E 3.76 F 3,58 G 3.64 H 3.69 I 3.73 J 3.70 K 3.62 L 3.72

M 3.88 N 3.89 O 3.93 P 3.76 Q 3.98 R 3.44 S 3.79 T 3.11 U 3.63 V 3,52 W 3,58 X 3,52 Y 2.93 Z 3.46 AA 3,50 BB 3.90 CC 2.06 DD 4,54

Creep Resistance

The creep resistance of the experimental alloys was determined using a long-term strength test at a temperature of 1800 ° F (982 ° C) under a load of 2.5 ksi (17 MPa). Under these conditions, a HASTELLOY X alloy with a high creep resistance (based on interpolation from Haynes International, Inc., publication No. H-3009C) is evaluated as having a creep time of 285 hours. For the purposes of the present invention, a minimum creep fracture time of 325 hours was established as a requirement, which would be a significant improvement over HASTELLOY X. It is useful to note that the temperature of 1800 ° F (982 ° C) during the test is higher than the predicted temperature solvus of the gamma-bar phase of the experimental alloys, thereby any effects of hardening by the gamma-bar phase should be negligible.

The time to failure from creep of the experimental alloys is shown in Table 5 along with data for several industrial alloys. All alloys from A to O, from R to Z, and BB were found to have creep times of more than 325 hours under these conditions, and therefore satisfy the requirement of the present invention with respect to creep resistance. Alloys P, Q, AA, CC, and DD were found to be inconsistent with the requirement for creep fracture resistance. For industrial alloys, alloy 617 and alloy 230 had acceptable creep times of 732.2 and 915.4 hours, respectively. In contrast, alloy 214 had a creep failure time of only 196.0 hours — significantly lower than the creep resistance requirement that defines the alloys of the present invention.

Table 5
The time to failure from creep at a temperature of 1800 ° F (982 ° C) / 2.5 ksi (17 MPa) Alloy Time to destruction (hours) A 1076.7 B 534.7 C 486.1 D 447.0 E 331.9 F 402.8 G 722.0 H 2051.1 I 360.0 J 1785.7 K 5645.5 L 566.7 M 1317.4 N 1197.3 O 340.3

P 134.3 Q 254.4 R > 500 S > 500 T > 330 U > 500 V 1624.0 W 693.8 X > 500 Y > 500 Z 909.4 AA 276.0 BB > 500 CC 224.3 DD 138.6 617 732.2 214 196.0 230 915.4 HASTELLOY X 285 (approximately)

Certain experimental alloys containing either hafnium or tantalum have been found to exhibit unexpectedly higher creep times than many other experimental alloys. For example, the hafnium-containing alloy K has a creep time of 5645.5 hours and the tantalum alloy N has a creep time of 1197.3 hours. A comparison of alloys with hafnium and tantalum additives and without additives is given in Table 6. For comparison purposes, the alloys are grouped according to their nominal base composition. A clear beneficial effect of hafnium and tantalum additives on the time to creep fracture can be seen for all base formulations. However, any beneficial effect of tantalum in terms of creep resistance to fracture should be weighed against any negative effects on machinability, as described earlier in this document.

Table 6
The effects of hafnium and tantalum additives on time to creep fracture
1800 ° F (982 ° C) / 2.5 ksi (17 MPa) Nominal base composition Alloy Adding Time to failure from creep (hours) Ni-16Cr-20Co-7.5Mo-3.5Al-1Fe C - 486.1 L 0.43 Hf 5645.5 K 0.71 Ta 566.7 Ni-16Cr-10Co-7.5Mo-3.5Al-10Fe P - 134.3 M 0.38 Hf 1317.4 N 0.78 Ta 1197.3 Ni-19.5Cr-10Co-7.5Mo-3.5Al-1Fe B - 534.7 V 0.48 Hf 1624.0 Z 1 Ta 909.4

As mentioned above, the experimental alloys P and Q, both of which contain about 10 wt.% Iron, did not meet the requirement for creep fracture resistance. These alloys contained additives of minor elements of tungsten and niobium, respectively. It is useful to compare these alloys with alloy G, which is similar to these two alloys, but without the addition of tungsten or niobium. Alloy G was found to have an acceptable creep failure time. Therefore, when the alloys from this series have an iron content in them at the upper limit of the range (~ 10 wt.%), Tungsten and niobium elements appear to have a negative effect on the time to failure from creep. However, when the iron content is lower, for example, in alloys I and T, tungsten additives do not lead to unacceptable values of the time to failure from creep. Similarly, niobium additives do not cause unacceptable creep times when the iron content is lower (T alloy). On this basis, the iron content in the alloys according to the present invention is limited to 5 wt.% Or less when tungsten or niobium is present as additives of minor elements. For alloys with an iron content of more than 5 wt.%, The amount of niobium and tungsten should be regulated to the level of impurities only (approximately 0.2 wt.% And 0.5 wt.% For niobium and tungsten, respectively).

Also mentioned above, alloys AA, CC, and DD do not satisfy the requirement for creep resistance. Alloy AA has a Mo content lower than that required by the present invention, while all other elements are present within their acceptable ranges. Therefore, it was found that for the required resistance to creep fracture, a critical minimum of the Mo content was necessary. Similarly, both CC and DD alloys have Al levels that are outside the range of the present invention, while all other elements are present within their acceptable ranges. The mechanisms responsible for the low creep resistance when the Al content is outside the ranges defined by the present invention are unclear.

Thermal stability

The thermal stability of the experimental alloys was tested using a tensile test at room temperature followed by thermal exposure at a temperature of 1400 ° F (760 ° C) for 100 hours. The degree of elongation under tension at room temperature (residual ductility) after thermal exposure can be taken as a measure of the heat resistance of the alloy. The exposure temperature of 1,400 ° F (760 ° C) was chosen because many nickel-based alloys have the lowest thermal stability around this temperature range. For acceptable thermal stability in the applications of interest, it was determined that a residual ductility of more than 10% is required. Residual ductility should preferably be above 15%. Of the 30 experimental alloys described here, 28 of them had a residual ductility of 17% or more — satisfactorily higher than the preferred minimum. The exceptions were BB and DD alloys, both having a residual ductility of less than 10%. BB alloy has a Mo level that is maximum for the alloys of the present invention, while all other elements are present within their acceptable ranges. Thus, it appears that this high level of Mo content caused poor thermal stability. Similarly, the DD alloy had an Al content higher than the maximum for the alloys of the present invention, while all other elements were present within their acceptable ranges. Thus, a high level of Al appears to be responsible for poor thermal stability.

Table 7
Thermal stability test Alloy Relative elongation,% (residual ductility), after exposure at a temperature of 1400 ° F (760 ° C) / 100 hours A 24 B 25 C 23 D 25 E 25 F 23 G 23 H 23 I 21 J 19 K 24 L 22 M twenty N 22 O 23

P twenty Q twenty R 21 S 17 T 23 U 23 V 21 W 23 X 21 Y 23 Z twenty AA 22 BB 2 CC 29th DD 7

According to a generalization of the test results for four key characteristics (oxidation resistance, machinability, creep resistance and thermal stability), alloys A to N, alloys R to X, and alloy Z (total 22) were found to be tested across all the four most important characteristics, and thus are considered as alloys according to the present invention. Also considered to be part of the present invention is alloy Y, which has been tested for resistance to creep fracture, modified by CHRT, and for thermal stability, but has not been tested for oxidation resistance (the level of aluminum in it indicates that alloy Y must have excellent oxidation resistance , exactly as directed by this description). Alloys O and DD did not pass the modified CHRT test, and thus were identified as having poor machinability (due to poor resistance to cracking during deformation aging). Alloys P, Q, AA, CC, and DD were found to not meet the requirement for creep fracture resistance. CC alloy did not meet the oxidation requirement. Finally, the BB and DD alloys did not satisfy the requirement for thermal stability. Therefore, alloys O, P, Q, AA, BB, CC, and DD (7 in total) are not considered alloys according to the present invention. These results are summarized in Table 8. In addition, seven different industrial alloys were discussed with experimental alloys. All seven industrial alloys were found to be inconsistent with one or many of the critical performance tests.

Table 8
Generalization of experimental alloys Alloy Did not pass the test (s) for the most important characteristics The alloy according to the present invention A YES B YES C YES D YES E YES F YES G YES H YES I YES J YES K YES L YES M YES N YES O Modified CHRT Test NO P Creep Resistance NO Q Creep Resistance NO R YES S YES T YES U YES V YES

W YES X YES Y YES Z YES AA Creep Resistance NO BB Thermal stability NO CC Oxidation, creep resistance NO DD Modified CHRT test, creep resistance, thermal stability NO

Suitable experimental alloys contained (in weight percent): from 15.3 to 19.9 chromium, from 9.7 to 20.0 cobalt, from 7.5 to 10.0 molybdenum, from 2.72 to 3.78 aluminum, from less than 0.1 up to 10.4 iron, from 0.085 to 0.120 carbon, as well as minor elements and impurities. In addition, suitable alloys had a member value of "Al + 0.56Ti + 0.29Nb + 0.15Ta" equation, which ranged from 2.93 to 3.89.

Perhaps the most important aspect of the present invention is a very narrow range of aluminum element contents. A critical aluminum content of at least 2.72 wt.% In these alloys is required to stimulate the formation of a protective oxide scale of aluminum oxide - necessary for their excellent oxidation resistance. However, the aluminum content must be adjusted to 3.9 wt.% Or less in order to maintain the workability of the alloys, as determined, in particular, by the resistance of the alloys to cracking during deformation aging. This careful control of the aluminum content is necessary for the alloys of the present invention. A narrow range of aluminum contents has also been found to be important for the resistance of these alloys to creep fracture, as well as for thermal stability. In addition to the narrow range of aluminum content, there are other factors critical to the present invention. They include cobalt and molybdenum additives, which contribute significantly to the increase in creep resistance to fracture, which is the most important characteristic of these alloys. In particular, it was found that a critical minimum level of molybdenum was needed in this particular class of alloys to provide sufficient resistance to creep fracture. Chromium is also important due to its contribution to oxidation resistance. Additives of certain minor elements can impart significant beneficial properties to the alloys of the present invention. This includes carbon, an important (and necessary) element for imparting resistance to creep fracture, grain refinement, etc. In addition, boron and zirconium, the presence of which is not necessary, can preferably be present due to their beneficial effects on fracture resistance during creep. Likewise, the presence of rare earth elements such as yttrium, lanthanum, cerium, etc., is preferred due to their beneficial effect on oxidation resistance. Finally, while all the alloys of the present invention have high creep resistance, the alloys with hafnium and / or lanthanum additives have been found to have unexpectedly distinct creep resistance.

The importance of certain elements for the ability of the alloys of the present invention to satisfy a combination of four key characteristics is illustrated by comparing the present invention with that described by Gresham in US Pat. No. 2,712,498, which partially matches the present invention. Gresham's patent describes wide ranges of elements that cover vast areas of the composition range. No attempt has been made to describe alloys that possess a combination of the four essential characteristics of the materials required in the present invention. In fact, Gresham's patent describes many alloys that do not satisfy the requirements of the present invention. For example, industrial alloy 263 was developed by Rolls-Royce Limited (which owns this patent), and has been used in the aerospace industry for decades. However, this alloy does not have the excellent oxidation resistance required by the present invention — as shown above in Table 2. In addition, Gresham et al. Do not provide any indication that a critical minimum level of Al is required for oxidation resistance. Another example is the DD alloy described in Table 1. This alloy falls within the scope of Gresham's patent. However, this alloy does not meet three of the four requirements of the present invention: resistance to creep fracture, resistance to cracking during deformation aging (as measured by the modified CHRT test), and thermal stability. The mismatch of the DD alloy with the requirement for cracking during deformation aging, for example, was shown in the present description as a result of too high levels of aluminum. Gresham et al. Provide no indication that there is a critical maximum level of aluminum (or maximum combined level of Al, Ti, Nb, and Ta) to avoid susceptibility to cracking during strain aging. A third example is that Gresham does not describe the need to limit the maximum molybdenum content to avoid poor thermal stability. In short, Gresham describes alloys that do not satisfy the combination of the four most important material characteristics described here, and does not provide any guidance on the most important compositional requirements required to combine these four characteristics, including, for example, a very narrow acceptable range of aluminum content.

The alloys according to the present invention should contain (in weight percent): from 15 to 20 chromium, from 9.5 to 20 cobalt, from 7.25 to 10 molybdenum, from 2.72 to 3.9 aluminum, carbon in an amount up to 0 , 15, and the remainder of nickel plus impurities of additives of minor elements. The ranges for the main elements are summarized in Table 9. In addition to carbon, minor element additives can also include iron, silicon, manganese, titanium, niobium, tantalum, hafnium, zirconium, boron, tungsten, magnesium, calcium, and one or more rare earth elements including, but not limited to, yttrium, lanthanum and cerium). The acceptable ranges of secondary elements are described below and summarized in Table 10.

Table 9
The ranges of the content of the main elements (in wt.%) Element Wide range Intermediate Range No. 1 Intermediate Range No. 2 Narrow Ni The rest of the amount The rest of the amount The rest of the amount The rest of the amount Cr from 15 to 20 from 16 to 20 from 17 to 20 from 17.5 to 19.5 Co from 9.5 to 20 from 15 to 20 from 17 to 20 from 17.5 to 19.5 Mo from 7.25 to 10 from 7.25 to 9.75 from 7.25 to 9.25 from 7.25 to 8.25 Al from 2.72 to 3.9 from 2.9 to 3.7 from 2.9 to 3.6 from 3.0 to 3.5

Elements titanium and niobium may be present, for example, to provide hardening, but their quantity should be limited due to their harmful effect on certain aspects of manufacturability. In particular, a too high content of these elements can increase the susceptibility of the alloy to cracking during strain aging. If present, titanium should be limited to a content of not more than 0.75 wt.%, And niobium to a content of not more than 1 wt.%. If they were not present as intentionally added additives, titanium and niobium could be present as impurities to a level of about 0.2 wt.% Each.

It was unexpectedly discovered that the presence of elements of hafnium and / or tantalum is associated with even longer times before the destruction of these alloys from creep. Therefore, one or both of the elements can be added to these alloys to further improve the creep resistance to fracture. Hafnium can be added at levels up to about 1 wt.%, While tantalum can be added at levels up to about 1.5 wt.%. For maximum efficiency, the sum of the tantalum and hafnium levels should be between 0.2 wt.% And 1.5 wt.%. If they were not present as intentionally added additives, hafnium and tantalum could be present as impurities to a level of about 0.2 wt.% Each.

To ensure workability, the amounts of certain elements that may or may not be present (more specifically, aluminum, titanium, niobium, and tantalum) should be limited in such a way as to satisfy the following additional ratio (where the amounts of elements are given in wt.%):

Al + 0.56Ti + 0.29Nb + 0.15Ta ≤ 3.9 [1]

In addition, boron may be present at a small but effective trace content of up to 0.015% by weight, to obtain certain favorable properties known in the art. Tungsten can be added to a content of about 2 wt.%, But if present as an impurity, typically would be contained in an amount of about 0.5 wt.% Or less. Iron may also be present as an impurity at levels of up to about 2% by weight, or may be deliberately added to higher levels to reduce the total cost of raw materials. However, iron should not be present in an amount of more than about 10.5 wt.%. If niobium and / or tungsten are present as minor added elements, the iron content should be even more limited to 5 wt.% Or less. To be able to remove oxygen and sulfur during the smelting process, these alloys typically contain small amounts of manganese up to about 1 wt.%, And silicon up to about 0.6 wt.%, And possibly traces of magnesium, calcium and rare earth elements (in including yttrium, cerium, lanthanum, etc.) to about 0.05 wt.% each. Zirconium may be present in the alloy as an impurity or deliberately added (for example, to improve the time to failure from creep), but its content in these alloys should be kept at 0.06 wt.% Or less to maintain workability, preferably 0.04 wt.% or less.

Table 10
Additives of minor elements (in wt.%) Element Wide range Intermediate Narrow range C present up to 0.15 present up to 0.12 from 0.02 to 0.12 Fe up to 10.5 up to 5 up to 2 Si up to 0.6 up to 0.5 up to 0.4 Mn up to 1 up to 1 up to 0.5 Ti up to 0.75 up to 0.75 from 0.2 to 0.5 Nb ^a up to 1 up to 1 ^s up to 1 ^d Ta up to 1.5 up to 1.5 ^s up to 1 ^d Hf up to 1 up to 1 ^s up to 0.5 ^d Zr up to 0.06 up to 0.04 present up to 0.04 B up to 0.015 up to 0.008 present up to 0.005 W ^a up to 2 up to 2 up to 0.5 Mg up to 0.05 up to 0.05 up to 0.05 Ca up to 0.05 up to 0.05 up to 0.05 REE ^b up to 0.05 each up to 0.05 each One or more are present up to 0.05 each ^and Alloys with Nb or W present in greater amounts than at impurity levels should also contain ≤ 5 wt.% Fe
^b Rare Earth Elements (REE) include one or more of Y, La, Ce, etc.
^c In the intermediate range, at least one element of niobium, tantalum and hafnium must be present, and the sum must be between 0.2 and 1.5
^d In a narrow range, at least one element of tantalum and hafnium must be present, and the amount should be between 0.2 and 1.5

A summary of acceptable levels of certain impurities is given in Table 11. Some of the elements listed in Table 11 (tantalum, hafnium, boron, etc.) may be present more as intentionally added additives than impurities; if this element is present as a deliberate additive, its quantity should correspond to the ranges defined in Table 10 rather than Table 11. Additional unspecified impurities may also be present, and are acceptable if they do not impair essential characteristics to a degree below certain standards.

Table 11
Permissible amounts of impurities (in wt.%) Impurity Content Allowed Fe 2 * Si 0.4 * Mn 0.5 * Ti 0.2 * Nb * 0.2 * Ta 0.2 * Hf 0.2 * Zr 0.05 * B 0.005 * W * 0.5 * Cu 0.5 S 0.015 P 0,03 * May be higher if it is a deliberate supplement (see Table 10)

From the information presented in the present description, the authors of the present invention may suggest that alloys with the compositions shown in Table 12 would also have the desired properties.

In addition to the four critical characteristics described above, other desirable properties of the alloys of the present invention would include: high tensile ductility in the state immediately after annealing, good resistance to hot cracking during welding, good resistance to thermal fatigue, and others.

Even though the tested specimens were limited to a deformable sheet, alloys should exhibit comparable properties in other forms obtained by plastic deformation (such as plates, rods, pipes, tubes, forgings, and wires), and in the forms of castings, sprayed coatings or powder metallurgy products, and namely, powder, pressed powder and sintered pressed powder. Therefore, the present invention encompasses all forms of alloy with a given composition.

The combination of characteristics such as excellent oxidation resistance, good machinability and good creep resistance shown by this alloy makes it particularly suitable for the manufacture of parts for gas turbine engines, and is particularly suitable for combustion chambers in these engines. Such parts, and engines containing such parts, can operate flawlessly at higher temperatures, and should have a longer service life than the same parts and engines currently available.

Although the authors of the present invention have disclosed certain preferred embodiments of the alloy, it should be clearly understood that the present invention is not limited to this, but can be practiced in a variety of ways within the scope of the claims of the following patent claims.

Claims (26)

1. An alloy based on Nickel-chromium-cobalt-molybdenum-aluminum, having a composition comprising in wt.%: from 15 to 20 chromium from 9.5 to 20 cobalt from 7.25 to 10 molybdenum from 2.72 to 3.9 aluminum up to 10.5 gland up to 0.15 carbon up to 0.015 bora up to 0.75 titanium up to 1 niobium up to 1.5 tantalum up to 1 hafnium up to 2 tungsten up to 1 manganese up to 0.6 silicon up to 0.06 zirconium up to 0.05 magnesium up to 0.05 calcium up to 0.05 rare earth element up to 0.5 copper up to 0.015 sulfur up to 0.03 phosphorus with the remaining amount of Nickel and impurities, while the alloy additionally satisfies the following compositional ratio, determined by the number of elements indicated in wt.%: Al + 0.56Ti + 0.29Nb + 0.15Ta ≤ 3.9. 2. The alloy according to claim 1, the total content of hafnium and tantalum is between 0.2 wt.% And 1.5 wt.%. 3. The alloy according to claim 1, containing titanium in an amount of from 0.2 to 0.75 wt.%. 4. The alloy according to claim 1, containing at least one element of hafnium and tantalum in the amount of hafnium from 0.2 wt.% Up to 1 wt.% And tantalum from 0.2 wt.% Up to 1.5 wt. % respectively. 5. The alloy according to claim 1, containing at least one element of hafnium, tantalum and niobium with their total amount between 0.2 wt.% And 1.5 wt.%. 6. The alloy according to claim 1, containing in wt.%: from 16 to 20 chromium from 15 to 20 cobalt from 7.25 to 9.75 molybdenum from 2.9 to 3.7 aluminum 7. The alloy according to claim 1, containing in wt.%:              from 17 to 20                                            chromium from 17 to 20 cobalt from 7.25 to 9.25 molybdenum from 2.9 to 3.6 aluminum 8. The alloy according to claim 1, containing in wt.%: from 17.5 to 19.5 chromium from 17.5 to 19.5 cobalt from 7.25 to 8.25 molybdenum from 3.0 to 3.5 aluminum 9. The alloy according to claim 1, containing in wt.%: up to 5 gland up to 0.12 carbon up to 0.008 bora up to 0.5 silicon up to 0.04 zirconium 10. The alloy according to claim 1, containing in wt.%: up to 2 gland from 0.02 to 0.12 carbon up to 0.005 bora from 0.2 to 0.5 titanium up to 0.5 manganese up to 0.4 silicon up to 0.04 zirconium 11. The alloy according to claim 1, which has an oxidation resistance determined by the average metal damage with a value of no higher than 2.5 mils / surface, when tested in an air stream at a temperature of 2100 ° F (1149 ° C) for 1008 hours. 12. The alloy according to claim 1, wherein the alloy has a CHRT test ductility value of over 7%. 13. The alloy according to claim 1, wherein the alloy has a time to failure of at least 325 hours when tested at a temperature of 1800 ° F (982 ° C) under a load of 2.5 ksi (17 MPa). 14. The alloy according to claim 1, wherein the alloy contains more than 5 wt.% Iron and at least one element of niobium up to 0.2 wt.% And tungsten up to 0.5 wt.%. 15. The alloy according to claim 1, containing in wt.%: from 15.3 to 19.9 chromium from 9.7 to 20.0 cobalt from 7.5 to 10.0 molybdenum from 2.72 to 3.78 aluminum from 0.1 to 10.4 gland from 0.085 to 0.120 carbon up to 0.005 bora up to 0.49 titanium up to 1.0 tantalum up to 0.48 hafnium up to 0.49 silicon up to 0.02 yttrium as a rare earth element up to 0.04 zirconium 16. The alloy according to claim 1, containing trace amounts of at least one element of magnesium, calcium and any rare earth element up to 0.05 wt.%. 17. The alloy according to claim 1, containing one or more of niobium up to 0.2 wt.%, Tungsten up to 0.5 wt.%, Copper up to 0.5 wt.%, Sulfur up to 0.015 wt.% and phosphorus up to 0.03 wt.%.